Methods of processing metallic materials

ABSTRACT

A method of processing a metallic material includes introducing an electrically conductive metallic material comprising at least one of a metal and a metallic alloy into a furnace chamber maintained at a low pressure relative to atmospheric pressure. A first electron field having a first area of coverage is generated using at least a first ion plasma electron emitter, and the material within the furnace chamber is subjected to the first electron field to heat the material to a temperature above a melting temperature of the material. A second electron field having a second area of coverage smaller than the first area of coverage is generated using a second ion plasma electron emitter. At least one of any solid condensate within the furnace chamber, any solidified portions of the electrically conductive metallic material, and regions of a solidifying ingot to the second electron field, is subjected to the second electron field, using a steering system.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of, and claims priority under35 U.S.C. §120 to, co-pending U.S. patent application Ser. No.12/546,785, filed on Aug. 25, 2009, which in turn is acontinuation-in-part of, and claims priority under 35 U.S.C. §120 to,U.S. patent application Ser. No. 12/055,415, filed Mar. 26, 2008, whichin turn claims priority under 35 U.S.C. §119(e) to U.S. ProvisionalPatent. Application Ser. No. 60/909,118, filed Mar. 30, 2007. Each ofthe referenced previously-filed applications is incorporated byreference herein in its entirety.

BACKGROUND OF THE TECHNOLOGY

1. Field of Technology

The present disclosure relates to equipment and techniques for meltingmetals and metallic alloys (hereinafter “alloys”). The presentdisclosure more specifically relates to equipment and techniquesutilizing electrons to melt or heat alloys and/or condensate formedwithin the melted alloys.

2. Description of the Background of the Technology

An alloy melting process involves preparing a charge of suitablematerials and then melting the charge. The molten charge or “melt” maythen be refined and/or treated to modify melt chemistry, removeundesirable components from the melt, and/or affect the microstructureof articles cast from the melt. Melting furnaces are powered either byelectricity or by the combustion of fossil fuels, and selection of asuitable apparatus is largely influenced by the relative costs andapplicable environmental regulations, as well as by the identity of thematerial being prepared. A variety of melting techniques and apparatusare available today. General classes of melting techniques include, forexample, induction melting (including vacuum induction melting), arcmelting (including vacuum arc skull melting), crucible melting, andelectron beam melting.

Electron beam melting typically involves utilizing thermo-ionic electronbeam guns to generate high energy substantially linear streams ofelectrons which are used to heat the target materials. Thermo-ionicelectron beam guns operate by passing current to a filament, therebyheating the filament to high temperature and “boiling” electrons awayfrom the filament. The electrons generated from the filament are thenfocused and accelerated toward the target in the form of a very narrow,substantially linear electron beam. A type of ion plasma electron beamgun also has been used for preparing alloy melts. Specifically, a “glowdischarge” electron beam gun described in V. A. Chernov, “PowerfulHigh-Voltage Glow Discharge Electron Gun and Power Unit on Its Base”,1994 Intern. Conf. on Electron Beam Melting (Reno, Nev.), pp. 259-267,has been incorporated in certain melting furnaces available fromAntares, Kiev, Ukraine. Such devices operate by producing a cold plasmaincluding cations which bombard a cathode and produce electrons that arefocused to form a substantially linear electron beam.

The substantially linear electron beams produced by the foregoing typesof electron beam guns are directed into the evacuated melting chamber ofan electron beam melting furnace and impinged on the materials to bemelted and/or maintained in a molten state. The conduction of electronsthrough the electrically conductive materials quickly heats them to atemperature in excess of the particular melting temperature. Given thehigh energy of the substantially linear electron beams, which may be,for example, about 100 kW/cm², linear electron beam guns are very hightemperature heat sources and are readily able to exceed the melting and,in some cases, the vaporization temperatures of the materials on whichthe substantially linear beams impinge. Using magnetic deflection orsimilar directional means, the substantially linear electron beams arerastered at high frequency across the target materials within themelting chamber, allowing the beam to be directed across a wide area andacross targets having multiple and complex shapes.

Because electron beam melting is a surface heating method, it typicallyproduces only a shallow molten pool, which may be advantageous in termsof limiting porosity and segregation in the cast ingot. Because thesuperheated metal pool produced by the electron beam is disposed withinthe high vacuum environment of the furnace melting chamber, thetechnique also beneficially tends to degas the molten material. Also,undesirable metallic and non-metallic constituents within the alloyhaving relatively high vapor pressures may be selectively evaporated inthe melting chamber, thereby improving alloy purity. On the other hand,one must account for the evaporation of desirable constituents producedby the highly-focused substantially linear electron beam. Undesirableevaporation must be factored into production and may significantlycomplicate alloy production when using electron beam melting furnaces.

Various melting and refining methods involve the electron beam meltingof feed stocks using thermo-ionic electron guns. Drip melting is aclassic method used in thermo-ionic electron beam gun melting furnacesfor processing refractory metals such as, for example, tantalum andniobium. Raw material in the form of a bar is typically fed into thefurnace chamber and a linear electron beam focused on the bar drip-meltsthe material directly into a static or withdrawal mold. When casting ina withdrawal mold, the liquid pool level is maintained on the top of thegrowing ingot by withdrawing the ingot bottom. The feed material isrefined as a result of the degassing and selective evaporation phenomenadescribed above.

The electron beam cold hearth melting technique is commonly used in theprocessing and recycling of reactive metals and alloys. The feedstock isdrip melted by impinging a substantially linear electron beam on an endof a feedstock bar. The melted feedstock drips into an end region of awater-cooled copper hearth, forming a protective skull. As the moltenmaterial collects in the hearth, it overflows and falls by gravity intoa withdrawal mold or other casting device. During the molten material'sdwell time within the hearth, substantially linear electron beams arequickly rastered across the surface of the material, retaining it in amolten form. This also has the effects of degassing and refining themolten material through evaporation of high vapor pressure components.The hearth also may be sized to promote gravity separation betweenhigh-density and low-density solid inclusions, in which case oxide andother relatively low-density inclusions remain in the molten metal for atime sufficient to allow dissolution while high density particles sinkto the bottom and become trapped in the skull.

Given the various benefits of conventional electron beam meltingtechniques, it would be advantageous to further improve this technology.

SUMMARY

According to one non-limiting aspect of the present disclosure, anapparatus for melting an electrically conductive metallic material isdescribed. The apparatus comprises a vacuum chamber, a hearth disposedin the vacuum chamber, and at least one ion plasma electron emitterdisposed in or adjacent the vacuum chamber and positioned to direct afirst field of electrons having a first cross-sectional area into thevacuum chamber. The first field of electrons has sufficient energy toheat the electrically conductive metallic material to its meltingtemperature. The apparatus further comprises at least one of a mold andan atomizing apparatus positioned to receive the electrically conductivemetallic material from the hearth, and an auxiliary ion plasma electronemitter disposed in or adjacent the vacuum chamber and positioned todirect a second field of electrons having a second cross-sectional areainto the vacuum chamber. The second field of electrons has sufficientenergy to at least one of heat portions of the electrically conductivemetallic material to at least its melting temperature, melt any solidcondensate within the electrically conductive metallic material, andprovide heat to regions of a forming ingot. The first cross-sectionalarea of the first field of electrons is different than the secondcross-sectional area of the second field of electrons. The second fieldof electrons emitted by the auxiliary ion plasma electron emitter issteerable.

According to another non-limiting aspect of the present disclosure, anapparatus for melting an electrically conductive metallic material isdescribed. The apparatus comprises a vacuum chamber, a hearth disposedin the vacuum chamber, and a melting device configured to melt theelectrically conductive metallic material. The apparatus furthercomprises at least one of a mold and an atomizing apparatus positionedto receive molten electrically conductive metallic material from thehearth, and an auxiliary ion plasma electron emitter disposed in oradjacent to the vacuum chamber and positioned to direct a focusedelectron field having a cross-sectional area into the vacuum chamber.The focused field of electrons has sufficient energy to at least one ofmelt portions of the electrically conductive metallic material, meltsolid condensate within the electrically conductive metallic material,and heat regions of a solidifying ingot. The focused field of electronsis steerable to direct the focused electron field toward at least one ofthe portions of the electrically conductive metallic material, the solidcondensate, and the solidifying ingot.

According to yet another non-limiting aspect of the present disclosure,an apparatus for melting an electrically conductive metallic material isdescribed. The apparatus comprises an auxiliary ion plasma electronemitter configured to produce a focused electron field including across-sectional profile having a first shape. The apparatus furthercomprises a steering system configured to direct the focused electronfield to impinge the focused electron field on at least a portion of theelectrically conductive metallic material to at least one of melt anysolidified portions of the electrically conductive metallic material,melt any solid condensate within the electrically conductive metallicmaterial, and provide heat to regions of a forming ingot.

According to still a further aspect of the present disclosure, a methodof processing a material is provided. The method comprises introducing amaterial comprising at least one of a metal and a metallic alloy into afurnace chamber maintained at a low pressure relative to atmosphericpressure, and generating a first electron field having a firstcross-sectional area using at least a first ion plasma electron emitter.The method further comprises subjecting the material within the furnacechamber to the first electron field to heat the material to atemperature above a melting temperature of the material, and generatinga second electron field having a second cross-sectional area using asecond ion plasma electron emitter. The method further comprisessubjecting at least one of any solid condensate within the material, anysolidified portions of the material, and regions of a solidifying ingotto the second electron field, using a steering system, to melt or heatat least one of the solid condensate, the solidified portions, and theregions of the solidifying ingot. The first cross-sectional area of thefirst electron field is different than the second cross-sectional areaof the second electron field.

According to a further aspect of the present disclosure, a method ofprocessing a material is provided. The method comprises introducing amaterial comprising at least one of a metal and a metallic alloy into afurnace chamber maintained at a low pressure relative to atmosphericpressure, and subjecting the material within the furnace chamber to amelting device configured to heat the material to a temperature above amelting temperature of the material. The method further comprisesgenerating a focused electron field using an auxiliary ion plasmaelectron emitter, and subjecting at least one of any solid condensatewithin the material, any solidified portions of the material, andregions of a solidifying ingot to the focused electron field, using asteering system, to melt or heat at least one of the solid condensate,the solidified portions, and the regions of the solidifying ingot.

According to yet a further aspect of the present disclosure, a method ofprocessing a material is provided. The method comprises generating afocused electron field including a cross-sectional profile having afirst shape using an auxiliary ion plasma electron emitter, and steeringthe focused electron field to impinge the focused electron field on thematerial and melt or heat at least one of any solid condensate withinthe material, any solidified portions of the material, and regions of asolidifying ingot.

According to still a further aspect of the present disclosure, a methodof generating an electron field to melt an electrically conductivematerial within a melting furnace is provided. The method comprisesproviding an anode having a first non-linear shape, applying a voltageto the anode, and producing a plasma containing positive cations at theanode. The method further comprises providing a cathode having a secondshape, positioning the cathode relative to the anode, and applying avoltage to the cathode. The voltage is configured to negatively chargethe cathode. The method further comprises accelerating the positivecations toward the cathode to generate free secondary electrons, andforming the electron field using the free secondary electrons. Theelectron field has a cross-sectional profile with a third shape. Thethird shape corresponds to the first non-linear shape of the anode.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of the apparatus and methods described hereinmay be better understood by reference to the accompanying drawings inwhich:

FIG. 1 is a schematic illustration in cross-section of an embodiment ofa conventional thermo-ionic electron beam gun melting furnace;

FIG. 2 is a simplified depiction of certain components of an embodimentof a wire-discharge ion plasma electron emitter;

FIG. 3 is a schematic illustration in cross-section of one non-limitingembodiment of an electron beam cold hearth melting furnace includingmultiple wire-discharge ion plasma electron emitters according to thepresent disclosure;

FIG. 4 is a schematic illustration of one non-limiting embodiment of awire-discharge ion plasma electron emitter;

FIG. 5 is a schematic illustration of one non-limiting embodimentaccording to the present disclosure of an electron beam melting furnaceincluding a wire-discharge ion plasma electron emitter as an electronsource;

FIG. 6 is a perspective view, partly in section, of one non-limitingembodiment of a wire-discharge ion plasma electron emitter that may beadapted for use in an electron beam melting furnace according to thepresent disclosure;

FIG. 7 is a diagram illustrating operation of the wire-discharge ionplasma electron emitter illustrated in FIG. 6;

FIG. 8 is a schematic illustration in cross-section of one embodiment ofan electron beam cold hearth melting furnace according to the presentdisclosure;

FIG. 9 is a schematic illustration in cross-section of one non-limitingembodiment of an electron beam cold hearth melting furnace includingmultiple ion plasma electron emitters and an auxiliary ion plasmaelectron emitter according to the present disclosure;

FIG. 10 is a schematic illustration in cross-section of one non-limitingembodiment of an electron beam cold hearth melting furnace including anauxiliary ion plasma electron emitter according to the presentdisclosure;

FIG. 11 is a schematic illustration of one non-limiting embodiment of asteering system for an auxiliary ion plasma electron emitter accordingto the present disclosure;

FIG. 12 is a schematic illustration from a top perspective of onenon-limiting embodiment of a steering system for an auxiliary ion plasmaelectron emitter according to the present disclosure;

FIG. 13 is a schematic illustration from a top view of one non-limitingembodiment of an auxiliary ion plasma electron emitter according to thepresent disclosure;

FIG. 14 is another schematic illustration from a top view of onenon-limiting embodiment of an auxiliary ion plasma electron emitteraccording to the present disclosure; and

FIG. 15 is still another schematic illustration from a top view of onenon-limiting embodiment of an auxiliary ion plasma electron emitteraccording to the present disclosure.

The reader will appreciate the foregoing details, as well as others,upon considering the following detailed description of certainnon-limiting embodiments of apparatuses and methods according to thepresent disclosure. The reader also may comprehend certain of suchadditional details upon carrying out or using the apparatuses andmethods described herein.

DETAILED DESCRIPTION OF CERTAIN NON-LIMITING EMBODIMENTS

In the present description of non-limiting embodiments, other than inthe operating examples or where otherwise indicated, all numbersexpressing quantities or characteristics of ingredients and products,processing conditions, and the like are to be understood as beingmodified in all instances by the term “about”. Accordingly, unlessindicated to the contrary, any numerical parameters set forth in thefollowing description are approximations that may vary depending uponthe desired properties one seeks to obtain in the apparatus and methodsaccording to the present disclosure. At the very least, and not as anattempt to limit the application of the doctrine of equivalents to thescope of the claims, each numerical parameter should at least beconstrued in light of the number of reported significant digits and byapplying ordinary rounding techniques.

Any patent, publication, or other disclosure material, in whole or inpart, that is said to be incorporated by reference herein isincorporated herein only to the extent that the incorporated materialdoes not conflict with existing definitions, statements, or otherdisclosure material set forth in this disclosure. As such, and to theextent necessary, the disclosure as set forth herein supersedes anyconflicting material incorporated herein by reference. Any material, orportion thereof, that is said to be incorporated by reference herein,but which conflicts with existing definitions, statements, or otherdisclosure material set forth herein is only incorporated to the extentthat no conflict arises between that incorporated material and theexisting disclosure material.

The present disclosure, in part, is directed to an improved design foran electron beam furnace for melting metals and metallic alloys and/orfor maintaining the materials in a molten state for use in preparingmetallic castings or powders. A conventional thermo-ionic electron beamgun melting furnace is schematically illustrated in FIG. 1. Furnace 110includes vacuum chamber 114 surrounded by chamber wall 115. Multiplethermo-ionic electron beam guns 116 are positioned outside and adjacentchamber 114 and direct discrete linear electron beams 118 into chamber114. Feed material in the forms of metallic bar 120 and alloying powder122 are introduced into chamber 114 by a conventional bar feeder 119 anda conventional particle or granule feeder 117, respectively. The linearelectron beam 118 of one of the electron beam guns 116 impinges on andmelts an end of bar 120, and the resulting molten alloy 124 falls intowater-cooled copper refining hearth 126 (a “cold hearth”) within chamber114. The thermo-ionic electron beam guns 116 are of a conventionaldesign and generate electrons by heating a suitable filament material.The guns 116 focus the generated electrons to a point, and the electronsare projected from the guns 116 in the form of a tightly focused,substantially linear beam. Thus, the electrons projected from the guns116 essentially impinge on the target as a point source. The heating ofthe target by the point source of electrons is facilitated by rasteringthe linear electron beams 118 across at least a portion of the targets,similar to the manner of rastering electrons across the phosphor screenof a cathode ray television tube. Rastering the substantially linearelectron beam 118 of a thermo-ionic electron beam gun 116 across the endregion of bar 120, for example, melts the bar 120.

With further reference to FIG. 1, the molten alloy 124 deposited inhearth 126 is maintained in a molten state by rastering certain of thesubstantially linear electron beams 118 across the surface of the moltenalloy 124 in a predetermined and programmed pattern. Powdered orgranulated alloying materials 122 introduced into the molten alloy 124by feeder 117 are incorporated into the molten material. Molten alloy124 advances across the hearth 126 and drops from the hearth by gravityinto a copper withdrawal mold 130. Withdrawal mold 130 includes atranslatable base 134 so as to accommodate the length of the growingingot 132. Molten alloy 124 initially collects in withdrawal mold 130 asmolten pool 131, and progressively solidifies into ingot 132.Impingement of electrons onto molten pool 131 by means of rastering oneor more of the substantially linear electron beams 118 across the pool'ssurface advantageously maintains regions of the pool 131, particularlyat the pool edges, in a molten state.

In furnaces utilizing one or more substantially linear electron beams toheat material in the furnace chamber, such as a conventionalthermo-ionic electron beam gun melting furnace, alloys includingvolatile elements, i.e., elements with relatively high vapor pressure atthe furnace melting temperatures, tend to boil off from the molten pooland condense on the relatively cold walls of the furnace chamber.(Common alloying elements having relatively high vapor pressures attemperatures commonly achieved by electron beam melting include, forexample, aluminum and chromium.) The substantially linear electron beammelting technique is particularly conducive to volatilization, which isa significant disadvantage of conventional electron beam furnaces whenalloying, as opposed to refining or purifying, for at least two reasons.First, the overall and localized chemical composition of the alloybecomes difficult to control during melting due to unavoidable losses ofhighly volatile elements from the molten pool. Second, the condensate ofthe vaporized elements tends to build up on the furnace walls over timeand may drop back into the melt, thereby contaminating the melt withinclusions and producing localized variations in melt chemistry.

Without intending to be bound by any particular theory, the inventorsbelieve that the foregoing disadvantages of conventional electron beammelting furnaces result from the action of conventional substantiallylinear electron beams on the materials processed within electron beamfurnaces. As suggested above in connection with the description of FIG.1, conventional electron beam cold hearth melting technology utilizessubstantially linear electron beams to both melt the raw materialsintroduced into the furnace and to maintain the temperature of themolten material as it flows along and over the cold hearth, and into thecasting mold. Such furnaces typically include multiple electron beamsources, wherein each source produces a substantially linear electronbeam that is essentially a point source. These “points” of intenseelectron concentration must be rastered rapidly over the areas to beheated so that the average temperature needed to melt the material andallow the molten material to adequately flow is reached throughout thetarget area. Because of the point source nature of the linear electronbeams, however, the spot at which the electron beam impinges on thealloy is heated to an extremely high temperature. This phenomenon oflocalized intense heating can be observed as visible white radiationemitted from the particular spot at which the electron beam impinges onthe solid or molten alloy within the furnace. It is believed that theintense superheating effect that occurs at these spots, along with thehigh vacuum maintained in the furnace chamber, readily evaporates therelatively volatile elements within the alloy, resulting in theexcessive evaporation of the volatile elements and concomitantcondensation on the chamber walls. As noted above, such condensationrisks contamination of the bath as the condensed material drops backinto the molten alloy, and this can result in, for example, markedcompositional heterogeneities in the cast ingots.

An improved design for an electron beam melting furnace described hereinutilizes one or more ion plasma electron emitters, such aswire-discharge ion plasma electron emitters, for example, as at least apart of the electron source in such a furnace. While wire-discharge ionplasma electron emitters are disclosed herein as exemplary ion plasmaelectron emitters, it will be understood that the other suitable ionplasma electron emitters (e.g., non-wire-discharge ion plasma electronemitters) can be used with the present disclosure, as discussed infurther detail below. As used herein, the terms “ion plasma electronemitter” and “wire-discharge ion plasma electron emitter” refer to anapparatus that produces a relatively wide, non-linear field of electronsby impinging positively charged ions onto a cathode and therebyreleasing a field of secondary electrons from the cathode. The electronbeam produced by an ion plasma electron emitter is not a linear beam,but instead is a three-dimensional field or “flood” of electrons that,when impinged on the target, covers a two-dimensional region that isvery large relative to the small point covered by impinging asubstantially linear electron beam onto the target. As such, theelectron field produced by ion the plasma electron emitters is referredto herein as a “wide-area” electron field, with reference to therelatively much smaller point of contact produced by conventionalelectron guns used in electron beam melting furnaces. Wire-discharge ionplasma electron emitters are known in the art (for use in unrelatedapplications) and are variously referred to as, for example, “wire ionplasma (WIP) electron” guns or emitters, “WIP electron” guns or emittersand, somewhat confusingly, as “linear electron beam emitters” (referringto the linear nature of the plasma-producing wire electrode(s) withincertain embodiments of the devices).

Wire-discharge ion plasma electron emitters are available in a varietyof designs, but all such emitters share certain fundamental designattributes. Each such emitter includes a plasma or ionization regionincluding a positive ion source in the form of an elongate wire anode toproduce plasma including cations, and a cathode that is spaced from andpositioned to intercept positive ions generated by the wire. A largenegative voltage is applied to the cathode, causing a fraction of thepositive ions in the plasma generated by the wire positive ion source tobe accelerated toward and to collide with the cathode surface such thatsecondary electrons are emitted from the cathode (the “primary”electrons being present within the plasma along with the positive ions).The secondary electrons produced from the cathode surface form anon-linear electron field that typically has the three-dimensional shapeof the positive ion plasma impacting the cathode. The secondaryelectrons are then accelerated from the vicinity of the cathode backtoward the anode, experiencing few collisions in the process of passingthrough the low-pressure gas within the emitter. By properly designingand arranging the various components of the wire-discharge ion plasmaelectron emitter, a wide field of energetic secondary electrons can beformed at the cathode and accelerated from the emitter and toward thetarget. FIG. 2 is a simplified depiction of components of awire-discharge plasma ion electron emitter, wherein a current is appliedto a thin wire anode 12 to generate plasma 14. Positive ions 16 withinplasma 14 accelerate toward and collide with negatively-charged cathode18, liberating wide-area secondary electron cloud 20, which isaccelerated in the direction of anode 12 by action of the electric fieldbetween the electrodes and toward the target.

According to one non-limiting embodiment according to the presentdisclosure, an apparatus for melting an electrically conductive metallicmaterial in the form of an electron beam melting furnace includes avacuum chamber (melting chamber) and a hearth disposed in the vacuumchamber and adapted to hold a molten material. At least onewire-discharge ion plasma electron emitter is disposed in or adjacent tothe vacuum chamber and is positioned to direct a non-linear, wide-areafield of electrons generated by the emitter into the chamber. Thewire-discharge ion plasma electron emitter produces a non-linear fieldof electrons having sufficient energy to heat the electricallyconductive metallic material to its melting temperature. A mold or othercasting or atomizing device is disposed in communication with thechamber and is positioned and adapted to receive material from thehearth. The furnace may be used to melt any material that may be meltedusing a conventional electron beam melting furnace, such as, forexample, titanium, titanium alloys, tungsten, niobium, tantalum,platinum, palladium, zirconium, iridium, nickel, nickel base alloys,iron, iron base alloys, cobalt, and cobalt base alloys.

Embodiments of an electron beam melting furnace according to the presentdisclosure may include one or more material feeders adapted to introduceelectrically conductive materials or other alloying additives into thevacuum chamber. Preferably, the feeders introduce the materials into thevacuum chamber in a position over or above at least a region of thehearth so that gravity will allow the materials, in solid or moltenform, to fall downward and into the hearth. Feeder types may include,for example, bar feeders and wire feeders, and the feeder type selectedwill depend upon the particular design requirements for the furnace. Incertain embodiments of the furnace according to the present disclosure,the material feeder and at least one of the one or more wire-dischargeion plasma electron emitters of the furnace are disposed so that theelectron field emitted by the wire-discharge ion plasma electron emitterat least partially impinges on the material introduced into the chamberby the feeder. If the material that is introduced into the vacuumchamber by the feeder is electrically conductive, then the electronfield, if of sufficient strength, will heat and melt the material.

The hearth incorporated in embodiments of a melting furnace according tothe present disclosure may be selected from the various hearth typesknown in the art. For example, the furnace may be in the nature of anelectron beam cold hearth melting furnace by incorporating a cold hearthor, more specifically, for example, a water-cooled copper cold hearth inthe vacuum chamber. As is known to those of ordinary skill, a coldhearth includes cooling means causing molten material within the hearthto freeze to the hearth surface and form a protective layer thereon. Asanother example, the hearth may be an “autogenous” hearth, which is ahearth that is plated with or fabricated from the alloy that is beingmelted in the furnace, in which case the bottom surface of the hearthalso may be water-cooled to prevent burn-through.

The particular hearth included in the vacuum chamber may include amolten material holding region, in which the molten material resides fora certain dwell time before passing to the casting or atomizing devicefluidly connected to the vacuum chamber. In certain embodiments of afurnace according to the present disclosure, the hearth and at least oneof the furnace's one or more wire-discharge ion plasma electron emittersare disposed so that the electron field emitted by the wire-dischargeion plasma electron emitter at least partially impinges on the moltenmaterial holding region. In this way, the electron field may be appliedto maintain the material within the molten material holding region in amolten state, and the heating action of the electron field may alsoserve to degas and refine the molten material.

Certain non-limiting embodiments of a furnace according to the presentdisclosure include a mold for casting the molten material. The mold maybe any suitable mold known in the art such as, for example, a staticmold, a withdrawal mold, or a continuous casting mold. Alternatively,the furnace may include or be associated with an atomization apparatusfor producing, for example, a powdered material from the moltenmaterial.

One particular non-limiting embodiment of an electron beam meltingfurnace according to the present disclosure includes a vacuum chamberand a hearth disposed in the vacuum chamber, wherein the hearth includesa molten material holding region. The furnace further includes one ormore wire-discharge ion plasma electron emitters disposed in or adjacentthe vacuum chamber. The hearth and the at least one wire-discharge ionplasma electron emitter are disposed so that an electron field producedby the emitter at least partially impinges on the molten materialholding region. A withdrawal mold communicates with the vacuum chamberand is positioned to receive molten material from the hearth. A leastone feeder is included in the furnace and is adapted to introducematerial into the vacuum chamber in a position over at least a region ofthe hearth.

Any suitable wire-discharge ion plasma electron emitter may be used inconnection with apparatus according to the present disclosure. Suitableembodiments of wire-discharge ion plasma electron emitters are disclosedin, for example, U.S. Pat. Nos. 4,025,818; 4,642,522; 4,694,222;4,755,722; and 4,786,844, the entire disclosures of which are herebyincorporated herein by reference. Suitable emitters include thosecapable of producing a non-linear, wide-area electron field that may bedirected into the vacuum chamber of the furnace and that will heatelectrically conductive feed materials placed into the furnace chamberto the desired temperature.

In one embodiment of a wire-discharge ion plasma electron emitter, theemitter includes a plasma region and a cathode region. The plasma regionincludes at least one elongate wire anode adapted to produce plasmaincluding positive ions. The cathode region includes a cathode which iselectrically connected to a high voltage power supply adapted tonegatively charge the cathode. In the wire-discharge ion plasma electronemitter, the electrode used to produce the plasma may be one wire ormultiple wires positioned along a length of the plasma region. At leasta portion of the cathode impacted by the positive ions is composed of amaterial suitable for generating electrons. Certain non-limitingembodiments of the cathode disposed in the cathode region of the emitteralso may include an insert, such as, for example, a molybdenum insert,having a high melting temperature and a low work function so as tofacilitate generation of electrons. The cathode and the anode arepositioned relative to one another so that the positive ions in theplasma generated by the wire anode accelerate toward and impinge on thecathode under influence of the electric field between the electrodes,liberating the wide-area field of secondary electrons from the cathode.

Certain non-limiting embodiments of the wire-discharge ion plasmaelectron emitter include at least one suitably electron transmissivewindow, such as a thin electron transmissive titanium or aluminum foil,that opens through a wall of the furnace vacuum chamber. Alternativematerials from which the electron transmissive window may be constructedinclude, for example, BN, diamond, and certain other materials composedof low atomic number elements. As discussed herein, other embodiments ofthe wire-discharge ion plasma electron emitter do not include anelectron transmissive window, in which case the plasma region of theemitter fluidly communicates with the vacuum chamber holding the moltenmaterial. In either case, the wide-area electron field derived entersthe furnace chamber and may be impinged on the material within thechamber. If an electron transmissive window does separate the interiorof the electron emitter from the vacuum chamber (as discussed furtherherein), then the electron field passes through the window as it isprojected from the electron emitter into the vacuum chamber. In certainnon-limiting embodiments of a wire-discharge ion plasma electronemitter, the high voltage power supply electrically coupled to thecathode powers the cathode to a negative voltage greater than 20,000volts. The negative voltage serves the functions of accelerating thepositive ions in the plasma toward the cathode and then repelling thesecondary electron field from the cathode and toward the anode.

An electron transmissive window is necessary if the pressure within thewire-discharge ion plasma electron emitter differs significantly fromthe pressure within the furnace chamber, in which case the foil windowserves to isolate the two adjacent regions of differing pressure. Anadvantage of wire-discharge ion plasma electron emitters relative tonon-gas containing electron emitters, such as thermo-ionic electron beamguns, is that wire-discharge ion plasma electron emitters must includegas within the plasma region to serve as the plasma source. Althoughwire-discharge ion plasma electron emitters can operate at very low gaspressures, such devices also can operate effectively at relatively highgas pressures. In contrast, conventional electron beam melting furnacescommonly operate at ultra low vacuum conditions, and in that case anelectron transmissive window would be necessary to separate the gasatmosphere within the wire-discharge ion plasma electron emitter and thenear vacuum environment within the furnace chamber. It appears, however,that volatile element evaporation within the furnace chamber may bereduced by increasing the gas pressure within the furnace chamber beyondthe ultra-low levels of conventional linear (thermo-ionic emitter)electron beam melting furnaces. Those conventional pressures levels aretypically within the range of 10⁻³ to 7.5μ (10⁻³ to 1 Pa) and do notexceed 15μ (2 Pa). Increasing pressure within the furnace chamber beyondconventional levels, i.e., to pressures exceeding 40μ (5.3 Pa), or morepreferably exceeding 300μ (40 Pa), increases the pressure at the surfaceof the molten material within the furnace and thereby reduces thedriving force for undesirable vaporization. For example, data presentedin H. Duval et al., “Theoretical and Experimental Approach of theVolatilization in Vacuum Metallurgy”, suggests that there is asignificant reduction in chromium vapor transport at 66.7 Pa (500 mTorr)argon relative to 4.27 Pa (35 mTorr) argon. Because wire-dischargeplasma ion electron emitters already require a partial gas pressureenvironment (typically of helium) to be operational, the presentinventors consider it possible that both the wire-discharge plasma ionelectron emitter and the furnace chamber could be operated atsubstantially the same pressure, wherein the pressure is sufficientlyhigh to allow the electron emitter to operate and also is higher than inconventional electron beam furnaces, thereby reducing undesirablevolatilization within the furnace chamber. In such case, the electrontransmissive window may be omitted such that the gas environment withinthe emitter and the furnace chamber is substantially the same.Alternatively, in another embodiment of a wire-discharge ion plasmaelectron emitter the electrons generated by the emitter pass through agas-impermeable window that is transparent to electrons, wherein thepressure of ionizable gas within the emitter is suitable for electronemitter operation and the furnace chamber is operated at a pressuregreater than conventional pressures in electron beam furnaces and issuitable for minimizing or reducing undesirable volatilization. It willbe understood that the reduction in undesirable elemental vaporizationwould be optimized by both utilizing one or more wire-discharge ionplasma electron emitters, which do not create points of intense heating,along with furnace chamber pressures greater than is conventional inelectron beam furnaces.

Further discussion of possible embodiments of an electron beam meltingfurnace and possible embodiments of a wire-discharge ion plasma electronemitter useful in connection with a furnace according to the presentdisclosure are provided below.

FIG. 3 schematically illustrates one possible non-limiting embodiment ofan improved electron beam melting furnace according to the presentdisclosure. Furnace 210 includes vacuum chamber 214 at least partiallydefined by chamber wall 215. Wire-discharge ion plasma electron emitters216 are positioned outside and adjacent chamber 214. The wire-dischargeion plasma electron emitters 216 project wide-area electron fields 218into the interior of the chamber 214. Similar to the conventionalfurnace 110 shown in FIG. 1, alloy bar 220 is introduced into chamber214 by a bar feeder 219. Molten alloy 226 is produced by impinging thewide-area electron field 218 of at least one wire-discharge ion plasmaelectron emitter 216 onto bar 220. The molten alloy 226 melted from bar220 drops into water-cooled copper hearth 224 and is resident in thehearth 224 for a certain dwell time, where it is heated, degassed, andrefined by one or more of the wide-area electron fields 218 produced byemitters 216. The molten alloy 226 ultimately drops from hearth 224 intocopper mold 230 and forms a molten pool 231. Molten pool 231 ultimatelyand progressively solidifies in mold 230 to form ingot 232. At least oneof the wide-area electron fields 218 preferably heats the molten alloywithin pool 231 in a manner advantageous to controlling thesolidification rate of the forming ingot 232.

As discussed above, the wire-discharge ion plasma electron emitters 216of furnace 210 are designed to generate a field or “flood” of energeticelectrons covering a wide area relative to the spot coverage of thesubstantially linear beam produced by electron beam guns used inconventional electron beam furnaces. The electron field emitters 216spread electrons over a wide area and impinge on the materials to bemelted and/or maintained in the molten state within the furnace 210,Because the electron field it produces will cover a wide area within thefurnace chamber, a wire-discharge ion plasma electron emitter willmaintain a more even temperature within the electron beam meltingfurnace relative to a conventional electron beam furnace, and alsodispenses with the need to raster a highly focused spot of electrons.Nevertheless, certain embodiments of the electron beam furnace accordingto the present disclosure may include components generating electricfields or other suitable components to steer the field of electronsgenerated by the one or more wire-discharge ion plasma electron emittersas desired. For example, in furnace 210 it may be desirable to rasterthe broad field produced by a wire-discharge ion plasma electron emitter216 from side-to-side to provide additional heat to edges of the hearth224. By flooding a relatively wide area with a field of energeticelectrons, rather than rastering a point source of electrons across thearea, the localized intense heating effect (e.g., power per unit area)associated with substantially linear electron beams that occurs whenusing conventional electron beam melting furnaces is significantlyreduced. This eliminates or at least significantly reduces the extent towhich relatively volatile alloying elements undesirably evaporate forthe reason that points of relatively extremely high temperature are notproduced. This, in turn, partially or wholly obviates the compositionalcontrol and contamination problems inherent in the conventional electronbeam furnace design.

As noted above, various embodiments of wire-discharge ion plasmaelectron emitters generally include one or more elongate wire anodesproducing positive ion plasma, wherein the plasma is impinged upon acathode to generate a field of secondary electrons that may beaccelerated to impinge on a target that is to be heated. A schematicrepresentation of one known design of a wire-discharge ion plasmaelectron emitter, previously used in other, unrelated, applications, isshown in FIG. 4. This emitter 310 includes an ionization or plasmaregion 314 in which a positive ion plasma is produced, and a cathoderegion 316 that includes cathode 318. The plasma region 314 is filledwith an ionizable gas at low pressure, and the gas is ionized in theplasma region to produce the cation-containing plasma. For example, theionization region 314 may be filled with helium gas at, for example,approximately 20 mTorr. A small diameter elongate wire anode 319 passesthrough a length of the plasma region 314. A positive voltage is appliedto wire anode 319 by power supply 322, and this initiates ionization ofthe helium gas into a plasma comprising helium cations and freeelectrons (the “primary” electrons). Once ionization of the helium gasis initiated, the plasma is sustained by applying a voltage to the thinwire anode 319. Positively charged helium ions within the plasma areextracted from the ionization chamber 314 through an extraction grid 326maintained at a high negative electrical potential and acceleratedthrough a high voltage gap into the cathode region 316, where thecations in the plasma impact high negative voltage cathode 318. Cathode318 may be, for example, a coated or uncoated metal or alloy.Impingement of helium ions on cathode 318 releases secondary electronsfrom cathode 318. The high voltage gap 328 accelerates the secondaryelectrons in a direction opposite the direction of movement of thehelium cations, through the extraction grid 326 and into the plasmaregion 314, and then through a thin metallic foil window 329 made ofmaterial relatively transparent to electrons. As noted above, dependingon the relative gas pressures within the electron emitter and thefurnace chamber, it may be possible to omit the foil window 329, inwhich case the electrons produced by the emitter would enter the furnacechamber directly.

The wire electrode 319 and the cathode 318 may be designed and arrangedto better promote movement of the positively charged helium ions to thecathode 318. Also, the cathode 318 and the extraction grid 326 may bedesigned and arranged to maximize secondary electron transmissionthrough the grid 326 and with a beam profile suitable for penetrationthrough foil window 329, if present. The wide-area field of energeticelectrons exiting the emitter 310 may be directed to impinge on a targetpositioned opposite foil window 329 and within the vacuum chamber of amelting furnace. Also, the window 329 may be sized to be as thin aspossible in order to maximize electron transmission from emitter 310. Analuminum-type or titanium-type foil having a thickness allowingsufficient electron transmission, while also maintaining a soft vacuumenvironment within the emitter 310, may be used as foil window 329, ifnecessary. Other suitably strong and acceptably electron transparentmaterials that may be used as a window in the apparatus, if present,will be known to those having ordinary skill. As discussed generallyherein, window 329 may be omitted if the pressure differences betweenthe interior of the emitter 310 and the vacuum chamber containing thetarget are not significant.

According to the present disclosure, one or more wire-discharge ionplasma electron emitters, such, for example, emitter 310, may beprovided to supply the energetic electrons into the vacuum chamber of anelectron beam melting furnace, as a substitute for electron beam gunsproducing a substantially linear electron beam. As shown in FIG. 5, onenon-limiting embodiment of an electron beam melting furnace 330according to the present disclosure includes one or more wire-dischargeion plasma electron emitters 310 positioned adjacent vacuum chamber 311.Wide-area electron field 332 exits emitter 310 through film window 329and floods at least a region of the surface of the molten alloy 334 inhearth 336, thereby heating the alloy to maintain it in a molten state.Because the electrons impinging on the alloy in hearth 336 are spreadacross a relatively wide area, the energy focused on the molten materialin any particular localized region is not great enough to result in aproblematic level of volatilization of elements from the alloy, therebyreducing or obviating the alloy contamination and heterogeneity problemsinherent in the use of conventional electron beam melting furnaces. Asnoted above, film window 329 may be omitted if the operating pressuredifferential between the emitter 310 and the vacuum chamber 311 is notsignificant. Also, as noted above, the vacuum chamber 311 preferably isoperated at a pressure higher than is conventional in order to furtherreduce or eliminate undesirable elemental vaporization, and in such casethe need for a film window partitioning the electron emitter from thefurnace chamber will, again, depend on the particular pressuredifferential inherent in the design. Optionally, components 340 formagnetically steering the wide-area electron field are provided so as toallow further improved control of the melting process within the vacuumchamber 311.

Although FIG. 5 provides a simplified view of one embodiment of awire-discharge ion plasma electron melting furnace according to thepresent disclosure including a single electron emitter, it will beapparent to those of ordinary skill that actual or alternate embodimentsof such an apparatus may have multiple wire-discharge ion plasmaelectron emitters. It also will be apparent that one or morewire-discharge ion plasma electron emitters may be incorporated in suchan apparatus to: (1) melt raw materials introduced into the furnace, inthe form of, for example, an alloy bar or wire; (2) maintain moltenalloy resident in the furnace hearth at a temperature above the alloymelting temperature (and possibly degas and/or refine the molten alloy);and (3) maintain desired regions of the molten pool on the surface ofthe incrementally advancing cast ingot in a molten state, therebyinfluencing ingot solidification rate in a desired manner. Also, incertain embodiments, one or more wire-discharge ion plasma electronemitters may be used along with one or more electron beam guns producingconventional substantially linear electron beams.

FIGS. 6 and 7 provide additional details related to one possiblenon-limiting embodiment of a wire-discharge ion plasma electron emitter510 that may be adapted for use as the source of energetic electrons inan embodiment of an electron beam melting furnace according to thepresent disclosure. FIG. 6 is a perspective view, partly in section, ofthe wire-discharge ion plasma electron emitter embodiment 510. FIG. 7 isa schematic diagram illustrating, in a simplified way, the operation ofemitter 510. Emitter 510 includes electrically grounded enclosure 513,which includes cathode region 511, ionization or plasma region 514, andelectron transmissive foil window 515. Elongate wire electrode 516extends through a length of ionization region 514. Foil window 515 iselectrically coupled to chamber 513 and thereby forms an anode thatoperates to accelerate electrons within chamber 513 therethrough to exitchamber 513 in the general direction of arrows “A”. Chamber 513 isfilled with helium gas at low pressure, such as 1-10 mTorr, and issupplied with the gas by gas supply 517. Gas supply 517 is connected toenclosure 513 by conduit 519, which passes through valve 521. A softvacuum environment is maintained in chamber 513 by pump 523, which isconnected to chamber 513 by conduit 524.

Cathode region 511 includes cathode 518, which in turn includes insert520 mounted on a lower surface thereof. The insert 520 may be composedof, for example, molybdenum, but may be composed of any material with asuitably high secondary electron emission coefficient. Cathode 518 issuitably uniformly spaced from the walls of enclosure 513 to preventPaschen breakdown. Cathode 518 is coupled to high voltage power supply522 by cable 525 which passes through insulator 526 and into resistor528. Power supply 522 supplies a high negative potential, for example,200-300 KV, to cathode 518. Cathode 518 and insert 520 may be suitablycooled, such as by, for example, circulating oil or another suitablecooling fluid through conduits 527.

Ionization region 514 includes a plurality of thin metallic ribs 530which are coupled both electrically and mechanically. Each rib 530includes a central cut-out region to allow wire electrode 516 to passthrough the ionization chamber 514. The sides of ribs 530 facing cathode518 form an extraction grid 534. The opposed side of all or a portion ofthe ribs 530 provide a support grid 536 for electron transmissive foilwindow 515. Cooling channels 540 may be provided to circulate a coolingfluid through and in the vicinity of ribs 530 to allow for heat removalfrom ionization region 514. Electron transmissive foil window 515, whichmay be composed of, for example, aluminum or titanium foil, is supportedon grid 536 and is sealed to enclosure 513 by an O-ring or otherstructures sufficient to maintain the high vacuum helium gas environmentwithin enclosure 513. In certain embodiments of emitter 510, a gasmanifold is provided to cool foil window 515, such as with pressurizednitrogen. As discussed generally herein, window 515 may be omitted ifthe pressure differences between the interior of the chamber 513 ofemitter 510 and the chamber containing the target of the electron fieldare not significant.

An electrical control device 548 is connected to wire electrode 516through connector 549. On activation of control device 548, wireelectrode 516 is energized to a high positive potential, and heliumwithin ionization region 514 is ionized to produce plasma includinghelium cations. Once the plasma is initiated in ionization region 514,cathode 518 is energized by power supply 522. Helium cations in theionization region 514 are electrically attracted to cathode 518 by theelectric field that extends from the cathode 518 into the plasma region514. The helium cations travel along the field lines, through theextraction grid 534, and into the cathode region 511. In the cathoderegion 511, the helium cations accelerate across the full potential ofthe electric field generated by the energized cathode 518 and forcefullyimpinge on the cathode 518 as a collimated beam of cations. Theimpacting cations free secondary electrons from the insert 520. Thesecondary electron field produced by the insert 520 is accelerated in adirection opposite the direction of travel of the helium cations, towardthe wire electrode 516, and through foil window 515, if present.

Means may be provided to monitor the actual gas pressure within thechamber 513 as changes in pressure may affect the density of the heliumion plasma and, in turn, the density of the secondary electron fieldgenerated at the cathode 518. An initial pressure may be set withinenclosure 513 by appropriately adjusting valve 521. Once thecation-containing plasma is initiated in plasma region 514, a voltagemonitor 550 may be provided to indirectly monitor the instantaneousquiescent pressure within the chamber 513. A rise in voltage isindicative of a lower chamber pressure. The output signal of the voltagemonitor 550 is used to control valve 521, through valve controller 552.The current supplied to wire electrode 516 by control device 548 also iscontrolled by the signal of voltage monitor 550. Utilizing the signalgenerated by voltage monitor 550 to control gas supply valve 521 andcontrol device 548 allows for a stable electron field output fromemitter 510.

The current generated by emitter 510 may be determined by the density ofthe cations impacting the cathode 518. The density of the cationsimpacting the cathode 518 may be controlled by adjusting the voltage onwire electrode 516 through control device 548. The energy of theelectrons emitted from the cathode 518 may be controlled by adjustingthe voltage on the cathode 518 through power supply 522. Both currentand energy of the emitted electrons can be independently controlled, andthe relationships between these parameters and the applied voltages arelinear, rendering control of the emitter 510 both efficient andeffective. In contrast, conventional thermo-ionic electron beam gunscannot be controlled in a corresponding linear manner when adjustingbeam parameters.

FIG. 8 is a schematic illustration of one embodiment of an electron beammelting furnace according to the present disclosure, wherein the furnace610 incorporates two wire-discharge ion plasma electron emitters 614,616 having a design as generally shown in FIGS. 6 and 7 and as discussedabove in connection with those figures. Furnace 610 includes vacuumchamber 620, material feeder 622, and casting or atomizing device 624.Current required for operation of emitters 614 and 616, as discussedabove, is fed to the emitters by power lines 626, and the interfacebetween emitters 614, 616 and the vacuum chamber 620 includes electrontransmissive foil windows 634, 636, which allow the electron fields 638generated by the emitters 614, 616 to enter the vacuum chamber 620. Thefoil windows 634, 636 may be omitted if the operating pressures withinthe emitters 614, 616 and the vacuum chamber are identical or do notsignificantly differ. Means 639 for magnetically steering electronfields 638 may be included within vacuum chamber 620 to provideadditional process control. A hearth 640, which may be, for example, acold hearth, is disposed in vacuum chamber 620. In operation,wire-discharge ion plasma electron emitters 614, 616 are energized andgenerate electron fields 618. An electrically conductive feed material644 is introduced into the vacuum chamber 620 by feeder 622, is meltedby electron field 638 emitted from emitter 614, and drops to hearth 640.Wide-area electron field 638 emitted by emitter 616 heats, degasses, andrefines the molten material 642 while resident in hearth 640. Moltenmaterial 642 advances along the hearth 640 and drops into casting oratomizing device 624 and is processed to a desired form.

The various non-limiting embodiments of the ion plasma electronemitters, such as the wire-discharge ion plasma electron emittersdiscussed above, for example, of the present disclosure may operate atvacuum pressures higher than the conventional thermo-ionic electron beamguns. Operation of a melting furnace at these higher pressures mayreduce the volatilization of volatile elements within the materialsbeing melted, as also discussed in further detail above. However, if anyof these volatile elements do boil off from the molten material, evenunder the higher vapor pressure conditions in the melting furnace, andcondense on the relatively cold chamber walls of the melting furnace,the condensate formed could detach from the chamber walls and fall intothe melt. Condensate falling into the melt may contaminate the melt withinclusions and/or produce localized variations in the melt chemistry.The inventor perceived that it would be advantageous to developapparatuses and methods to prevent or inhibit the formation of suchcondensate in ion plasma electron emitter melting furnaces and othertypes of melting furnaces.

As such, the present disclosure, in part, is directed to an apparatusincluding at least one auxiliary electron emitter in the form of an ionplasma electron emitter, such as a wire-discharge ion plasma electronemitter, for example, that is configured to be used with a meltingfurnace comprising one or more other ion plasma electron emitters, suchas wire-discharge ion plasma electron emitters, for example, for meltingan electrically conductive metallic material. Another non-limitingembodiment according to the present disclosure is directed to anapparatus including at least one auxiliary electron emitter in the formof an ion plasma electron emitter, such as an auxiliary wire-dischargeion plasma electron emitter, for example, that is configured to be usedwith a melting furnace comprising one or more thermo-ionic electron beamguns and/or other melting devices. Because the auxiliary electronemitter according to the present disclosure comprises an ion plasmaelectron emitter as an electron source, it is referred to herein as anauxiliary ion plasma electron emitter, as an auxiliary electron emitter,or, in one exemplary embodiment, as an auxiliary wire-discharge ionplasma electron emitter. Those of skill in the art will recognize, uponreview of the present disclosure, that although the wire-discharge ionplasma electron emitters and the auxiliary wire-discharge ion plasmaelectron emitters are discussed in detail herein, any other suitable ionplasma electron emitters or auxiliary ion plasma electron emitters canbe used and are within the scope of the present disclosure. Examples ofother suitable ion plasma electron emitters and other suitable auxiliaryion plasma electron emitters are discussed in further detail below.Further, as discussed below, the “wire” of the wire-discharge ion plasmaelectron emitters and the auxiliary wire-discharge ion plasma electronemitters can be formed into any suitable shape, such as circular-shaped,linear-shaped, square-shaped, rectangular-shaped, ovate-shaped,elliptical-shaped, or triangular-shaped, for example, to form electronfields having variously shaped cross-sectional areas or profiles.

In certain non-limiting embodiments, the auxiliary electron emitteraccording to the present disclosure may comprise a wire-discharge ionplasma electron emitter that is configured and functions in a way thatis the same as or is similar to the various wire-discharge ion plasmaelectron emitters discussed above. For example, the auxiliarywire-discharge ion plasma electron emitter may comprise a plasma regionincluding a wire electrode, such as an elongate wire anode, configuredto produce plasma including positive ions, and a cathode regionincluding a cathode electrically connected to a high voltage powersupply configured to negatively charge the cathode. In variousnon-limiting embodiments, the cathode may be positioned relative to thewire electrode so that positive ions generated by the wire electrode areaccelerated toward and impinge on the cathode, liberating electrons fromthe cathode and creating an electron field, such as a focused electronfield, for example. The focused electron field can beelectromagnetically “focused” and/or directed to appropriate regions ofthe melting chamber through the use of electromagnets, for example. Forpurposes of the present disclosure, the phrase “focused electron field”means a field having a cross-sectional area, at least after beingelectromagnetically focused, that is smaller than a cross-sectional areaof a field of electrons emitted by the various ion plasma electronemitters discussed above (referred to hereafter as “wide-area electronfield”). The focusing of the electron fields can make the electronfields higher powered by providing a greater electron density per unitarea, for example. It will be understood that when referring to a“cross-sectional area” or a “cross-sectional profile” of an electronfield in the present disclosure, that the cross-sections will be takenin a direction substantially perpendicular to a path of travel of thevarious electron fields at a particular instant in time.

In certain non-limiting embodiments, the auxiliary wire-discharge ionplasma electron emitter may operate at a higher power than the variouswire-discharge ion plasma electron emitters discussed above to providehigher power, higher electron density, and/or focused electron fieldswhen compared to the lower powered, less dense, and less focusedelectron fields generated by the various wire-discharge ion plasmaelectron emitters discussed above. In one exemplary embodiment, if thecathode is charged to a higher negative voltage, then the electronenergy of the electron field will be greater owing to the higherelectron energy of free electrons coming off of the cathode.Additionally, if a higher voltage is applied to the anode, then thedensity of the electrons of the electron field will be greater owing toa greater number of ions being produced at the anode. In anotherexemplary embodiment, the higher voltage can be applied to both theanode and the cathode (negative voltage) to produce a higher energy anddenser electron field. This electron field can then beelectromagnetically focused and/or directed to portions of the melt. Assuch, the focused electron field of such embodiments may be used to meltcondensate, condensate within the melt, solidified portions within themelt, and/or unmelted portions within the melt, for example. The focusedelectron field may also be used to maintain the molten material within avacuum chamber of a melting furnace at a suitable temperature at variousregions of the vacuum chamber. The higher energy, denser, and/or morefocused electron field may be used because of the limited residence timeof the condensate, solidified portions, and/or unmelted portions withinthe melt in regions of the vacuum chamber. As such, it is desirable tomelt the condensate, solidified portions, and/or unmelted portions priorto them moving into another region of the vacuum chamber. The auxiliarywire-discharge ion plasma electron emitter may also be adapted orsteerable so that the direction of the focused electron field generatedby the auxiliary electron emitter may be moved and/or directed to anyother appropriate region within the vacuum chamber of the meltingfurnace, for example, so that it impinges on a particular desiredtarget. In one non-limiting embodiment, the focused electron field maybe impinged on a region of a forming or solidifying ingot toadvantageously influence solidification kinetics of the molten pool 231and, therefore, characteristics of the solid ingot 232, for example.

Those of skill in the art will recognize that the auxiliarywire-discharge ion plasma electron emitters of the present disclosuremay comprise, for example, any suitable features of the variouswire-discharge ion plasma electron emitters described above. As such,and for sake of brevity, those features are not specifically recitedagain in this section with respect to the auxiliary wire-discharge ionplasma electron emitters. It will be understood that any component,element, and/or portion in FIGS. 9-15 having a reference number that isthe same as any component, element, and/or portion in FIGS. 1-8,described above, may be the same or similar and may have the same orsimilar structure and/or function. Also, any of the components,elements, and/or portions described above with respect to the variousexemplary embodiments illustrated in FIGS. 1-8 may be used inconjunction with the various exemplary embodiments described in FIGS.9-15.

In one non-limiting embodiment, referring to FIG. 9, an auxiliarywire-discharge ion plasma electron emitter 700 may be positioned in oradjacent to a vacuum chamber 214 of a melting furnace 210. The auxiliarywire-discharge ion plasma electron emitter 700 may be used inconjunction with or independent of the one or more wire-discharge ionplasma electron emitters 216. In one non-limiting embodiment, one ormore wire-discharge ion plasma electron emitters 216 may be used to heatand melt the bar 220 of metallic material, and one or morewire-discharge ion plasma electron emitters 216 may be used to heat andrefine molten metallic material 226 in the hearth 224. In certainnon-limiting embodiments, the auxiliary wire-discharge ion plasmaelectron emitter 700 may be used to melt any condensate formed on thewalls 215 of the vacuum chamber 214 and/or melt any solidified portions,including condensate, in the melted metallic material present in thehearth 224. In other non-limiting embodiments, the auxiliarywire-discharge ion plasma electron emitter can be used to heat themolten pool 231 or other regions of the forming or solidifying ingot232, as discussed herein.

Accordingly, in various non-limiting embodiments, the auxiliarywire-discharge ion plasma electron emitter 700 may be adapted toselectively melt condensate formed on the chamber wall 215 and therebyprevent or reduce the possibility of solid condensate detaching from thechamber wall 215 and falling into the molten material 226. Also, invarious non-limiting embodiments, the auxiliary wire-discharge ionplasma electron emitter 700 may be adapted to provide additional heatingat desired regions along the hearth 224, for example, to melt solids,such as the condensate, for example, within the molten material 226and/or to maintain the molten material 226 in a molten state at one ormore regions along the hearth 224. Additionally, in various non-limitingembodiments, the auxiliary wire-discharge ion plasma electron emitter700 may be adapted to heat regions of the molten pool 231 andadvantageously influence solidification kinetics of the molten pool 231and characteristics of the ingot 232. Application of a focused electronfield emitted by the auxiliary wire-discharge ion plasma electronemitter 700 to the molten pool 231 may improve the surface finish of theingot 232 during withdrawal, minimize metal tearing within the ingot232, and/or advantageously influence the resulting microstructure of theingot 232, for example.

In one non-limiting embodiment, still referring to FIG. 9, the auxiliarywire-discharge ion plasma electron emitter 700 is configured to producea focused electron field, such as focused electron field 702, forexample. This focused electron field 702 is a three-dimension field ofelectrons and, therefore, when impinging on a target, covers a regionmuch greater than the essentially linear “beam” of electrons generatedby a conventional thermo-ionic electron beam gun. The focused electronfield 702, however, may cover a region having an area less or much lessthan the region covered by the relatively wide-area electron field 218,for example, emitted by the wire-discharge ion plasma electron emitter216, as discussed above. In one non-limiting embodiment, the focusedelectron field 702 may have an area of 0.5 square inches to 50 squareinches, alternatively 1 square inch to 30 square inches, andalternatively 1 square inch to 20 square inches, for example, when itimpinges on a target in the vacuum chamber of a melting furnace. Thefocused electron beam, in certain embodiments, is steerable, or at leastdirectable, such that it can be impinged on condensate or other solidportions within the melt. Those of skill in the art, upon consideringthe present disclosure, will recognize that the focused electron fieldmay have any suitable cross-sectional areas or profiles for particularapplications.

In one non-limiting embodiment, the cross-sectional area and/or thecross-sectional shape of the focused electron field 702 may be afunction of the size and shape of the anode and/or the cathode of anauxiliary electron emitter, for example. For example, in certainnon-limiting embodiments, the anode and the cathode are of a relativelylarge size and the focused electron field 702 covers a relatively largecross-sectional area. This relatively large cross-sectional area,however, is generally smaller than a cross-sectional area of thewide-area electron field, but substantially larger than the essentially“spot” coverage of the substantially linear “beam” emitted by aconventional thermo-ionic electron emitter. The focused electron fieldcan also comprise various cross-sectional shapes, such as circular orsquare, for example, based on the shape of the anode. In onenon-limiting embodiment, an anode having a circular shape can be used,in conjunction with a cathode, to produce a focused electron fieldhaving a circular or substantially circular cross-sectional shape, forexample.

In one non-limiting embodiment, again referring to FIG. 9, thewire-discharge ion plasma electron emitters 216 may emit at least onefirst field of electrons 218 (i.e., a wide-area electron field) having afirst cross-sectional area. The auxiliary wire-discharge ion plasmaelectron emitter 700 may emit a second field of electrons, such as thefocused electron field 702, having a second cross-sectional area. Invarious embodiments, the first cross-sectional area may be larger than,the same as, or smaller than the second cross-sectional area. Inconnection with describing a particular field of electrons, the term“area” may refer to an area of coverage of the field of electrons whenthe field of electrons is impinged upon condensate, solid portionswithin the molten material, regions of a forming or solidifying ingot,and/or other regions of the vacuum chamber.

In one non-limiting embodiment, the focused electron field 702 emittedby the auxiliary wire-discharge ion plasma electron emitter 700 has asmaller cross-sectional area than the wide-area electron field emittedby the wire-discharge ion plasma electron emitter 216. In thatembodiment, the focused electron field 702 may be more focused andoptionally of a higher power (e.g., higher electron density and/orhigher energy electrons) than the wide-area electron field emitted bythe wire-discharge ion electron emitter 216. The higher electron densityof the focused electron field 702 can be created by applying a highervoltage to the anode, for example, to create more ions at the anode and,therefore, create more secondary electrons coming from the cathode. Thepower of the focused electron field 702 can be increased or decreasedfor suitable melting of condensate or solid portions of the melt. Insuch an embodiment, the electron accelerating voltage (kV) of thecathode and the electron current (kW) can be varied for suitablemelting, for example. In one non-limiting embodiment, the electroncurrent (kW) can be increased to cause faster melting. In othernon-limiting embodiments, the focused electron field 702 can also befurther focused to increase the density of the electrons within thefocused electron field 702 and, thereby, cause faster melting.

In one non-limiting embodiment, the focused electron field 702 may bedirected toward any condensate, solidified portions, and/or unmeltedportions within the molten alloy 226 or the molten pool 231. Inaddition, in certain embodiments, the focused electron field 702 may bedirected toward to the molten pool 231 to influence the solidificationof the molten material into the ingot 232. The focused electron field702 may also be directed to regions of the chamber walls 215 havingcondensate thereon to melt the condensate or to other regions of themelting furnace 210.

With reference again to FIG. 9, the focused electron field 702 may bedirected by a steering system, such as, for example, steering system704. The steering system 704 may generate and manipulate one or moreelectric fields and/or magnetic fields, for example, to steer thefocused electron field 702 to impinge it on a desired region or thingwithin the vacuum chamber 214 of the melting furnace 210. Conventionaltechniques and apparatus known to those having ordinary skill in the artfor manipulating the direction of electron fields, such as magneticdeflection, for example, may be suitably adapted for use in the steeringsystem 704. Given that such techniques and apparatus for manipulatingelectron fields are known to those having ordinary skill in the art,they are not described in detail herein. Also, for example, the steeringsystem 704 may be designed to selectively raster the focused electronfield 702 generated by the auxiliary ion plasma electron emitter 700about a particular region within the vacuum chamber 214 of the meltingfurnace 210. Various conventional techniques and apparatus are known tothose having ordinary skill in the art for rastering electron beams andmay be suitably adapted for use in the steering system 704. Given thatsuch techniques and apparatus for rastering electron fields are known tothose having ordinary skill, they are not described in detail herein. Inone non-limiting embodiment, rastering the focused electron field 702may quickly move the field over a region of condensed material on thechamber wall 215 to melt the condensate, over a solidified portion orunmelted portion of material within the hearth 224 to melt the material,and/or over the molten pool 231 to influence the solidification of theforming ingot 232 as desired. Rastering the focused electron field 702may also be employed to eliminate or help to at least reduce thepossibility that an excess of power or energy will be transferred by thefocused electron field 702 to the condensate, the solidified portions,and/or the molten material on which the focused electron field 702impinges. Application to the condensate, the solidified portions, and/orthe molten material of an excess of electron energy/unit area and/or anelectron density/unit area could vaporize the volatile elements withinthe condensate or material, which could exacerbate condensation ofmaterial on the chamber walls 215. In one non-limiting embodiment, thesteering system 704 may be used to direct the focused electron field 702to any suitable location within the melting furnace 210.

In one-non-limiting embodiment, a steering system for the focusedelectron field 702 can be selectively operated such that an operator canspecifically direct the focused electron field 702 to particularportions of the melt that require melting and/or reheating. Such aselective steering system can move the steering devices 704, or othersteering devices, to thereby direct the focused electron field 702 tosuitable regions within the vacuum chamber, such as over condensateparticles within the melt. In other non-limiting embodiments, varioussteering devices, such as electromagnets, for example, can be properlyarrayed within the vacuum chamber such that the focused electron field702 can be directed to a predetermined region of the vacuum chamberand/or can be selectively movable by an operator between a firstpredetermined region of the vacuum chamber and a second predeterminedregion of the vacuum chamber, for example.

FIG. 10 illustrates another non-limiting embodiment of an auxiliary ionplasma electron emitter 700′, such as a wire-discharge ion plasmaelectron emitter, for example, included in an electron beam meltingfurnace 610. Various elements of the electron beam melting furnace 610are identified by reference numbers included in FIG. 8 and describedabove. The auxiliary ion plasma electron emitter 700′ may emit a focusedelectron field 702′, similar to the focused electron field 700, that maybe impinged on the molten material 642 disposed in the hearth 640 and/orsolids (such as, for example, condensate that has fallen from thechamber wall) within the molten material 642. In one non-limitingembodiment, the auxiliary ion plasma electron emitter 700′ may include asteering system 704′, which may have a construction as discussed above,for example.

In one non-limiting embodiment depicted schematically in FIG. 11, anexemplary steering system is adapted for use in conjunction with theauxiliary ion plasma electron emitter 700 or 700′ (referred tocollectively as “700”). The steering system for the focused electronfield 702 of the auxiliary ion plasma electron emitter 700 may comprisea first magnetic and/or electric steering device 706 and a secondmagnetic and/or electric steering device 708. The first steering device706 may be positioned on a first side of the focused electron field 702,and the second steering device 708 may be positioned on a second side ofthe focused electron field 702. The first and second steering devices706 and 708 may be configured to generate a magnetic and/or electricfield therebetween that is translatable to direct the focused electronfield 702 in a desired direction. As a result, the first and secondsteering devices 706 and 708 may be used to direct the focused electronfield 702 to a desired region or location within a vacuum chamber of amelting furnace. The steering system can include additional steeringdevices such that the focused electron field 702 can be directed in anysuitable direction within the vacuum chamber. The exemplary steeringsystem illustrated in FIG. 11 can also be used to focus or further focusthe focused electron field 702.

Another non-limiting embodiment of a steering system for the focusedelectron field 702 is schematically depicted in FIG. 12. In such anembodiment, the steering system may comprise more than one steeringdevice 710 positioned about the focused electron field 702 (notillustrated in FIG. 12, but projecting in a path into and generallyperpendicular to the page). Similar to the first and second steeringdevices 706 and 708 above, the steering devices 710 may each generate amagnetic and/or an electric field configured to act upon the focusedelectron field 702. By providing more than one, more than two, or morethan three, for example, steering devices 710, the focused electronfield 702 may be precisely directed to any desired region or objectwithin the vacuum chamber of the melting furnace. Those of skill in theart will recognize that other conventional systems for steering electronfields may be used in conjunction with the auxiliary ion plasma electronemitters described herein to steer a direction of the focused electronfield 702. Similar to the exemplary steering system of FIG. 11, theexemplary steering system of FIG. 12 can also be used to focus orfurther focus the focused electron field 702.

In one non-limiting embodiment, an apparatus for melting an electricallyconductive metallic material may comprise an auxiliary wire-dischargeion plasma electron emitter configured to produce a focused electronfield including a cross-sectional profile having a first shape and asteering system configured to direct the focused electron field toimpinge on at least a portion of the electrically conductive metallicmaterial to melt any solid condensate or other solids therein. Thefocused electron field may also be directed by the steering system ontothe molten pool or other regions of a forming or a solidifying ingot toadvantageously influence solidification kinetics of the ingot. In such anon-limiting embodiment, the apparatus may comprise a wire electrodehaving a second shape and a cathode having a third shape. In at leastone embodiment, the first shape may be substantially similar to or thesame as the second shape and/or the third shape. The first shape of thecross-sectional profile of the electron field may be substantiallycircular-shaped, triangular-shaped, rectangular-shaped, square-shaped,elliptical-shaped, or ovate-shaped, for example, or may be any othersuitable shape. Thus, those of ordinary skill in the art will recognizethat the first shape of the cross-sectional profile of the focusedelectron field may be any shape suitable for melting condensate, meltingsolids within the melt, melting unmelted portions of metallic materialwithin the melt, and/or heating the molten pool of the solidifying ingotin a desired manner. If, for example, a focused electron field having asubstantially triangular-shaped cross-sectional profile is desired, theauxiliary wire-discharge ion plasma electron emitter may include asubstantially triangular-shaped wire electrode and/or a substantiallytriangular-shaped cathode.

In one non-limiting embodiment, the ion plasma electron emitters or theauxiliary ion plasma electron emitters may comprise an anode (or cationproducing electrode) other than a wire-like anode. In such anembodiment, the anode may be an electrically conductive thin plate,sheet, or foil configured to allow the focused electron field emittedfrom the cathode to readily pass therethrough. In other embodiments, theanode may comprise any other suitable configuration. The electricallyconductive thin plate, sheet, or foil anode may comprise any suitableshape such as substantially circular-shaped, square-shaped,rectangular-shaped, triangular-shaped, elliptical-shaped, ovate-shaped,or any other suitable shape. By providing an anode in these variousshapes, or other various shapes, the shapes of the cross-sectional areasor profiles of the wide-area electron field and/or the focused electronfield may be controlled. For example, to create a focused electron fieldhaving a circular cross-sectional shape, a circular thin plate, sheet,or foil anode may be used. In one non-limiting embodiment, the cathodeof the ion plasma electron emitter or the auxiliary ion plasma electronemitter may also be comprised of any electrically conductive thin plate,sheet, or foil of any suitable dimensions. This electrically conductivethin plate, sheet, or foil of the cathode may comprise a similar shapeas the shapes of the various anodes discussed above. In one non-limitingembodiment, the shape of the cathode may work in conjunction with theshape of the anode to produce a wide-area electron field or a focusedelectron field having variously shaped cross-sectional areas orprofiles. Although the ion plasma electron emitters producing thewide-area electron fields are discussed above with reference to anexemplary wire-discharge ion plasma electron emitter, those of skill inthe art will recognize that ion plasma electron emitters having‘non-wire’ or ‘non-straight wire’ anodes may be used and are within thescope of the present disclosure.

Similar to the various wire-discharge ion plasma electron emittersdescribed above, various non-limiting embodiments of the auxiliarywire-discharge ion plasma electron emitters may include one or moreelongate wire anodes configured to produce a cation-containing plasma,wherein the plasma cations are impinged on a cathode to generate a fieldof secondary electrons (i.e., the focused electron field) that areaccelerated to impinge on a target, such as condensate, for example,that is to be melted to reduce solid inclusions within the melt. Theelongate wire anode may have a length dimension that is substantiallygreater than its thickness dimension. Although described as “elongate”,the elongate wire anode can be formed into any suitable shape. Theauxiliary wire-discharge ion plasma electron emitter may be constructedin a way that is substantially the same or generally similar to thatdescribed above with reference to the various wire-discharge ion plasmaelectron emitters. As such, the above description of the variouswire-discharge ion plasma electron emitters is incorporated into thepresent description of the design of the auxiliary wire-discharge ionplasma electron emitter. In addition, a description of the manner ofconstruction and operation of certain non-limiting embodiments of theauxiliary ion plasma electron emitter according to the presentdisclosure follows.

As noted above, an auxiliary ion plasma electron emitter according tothe present disclosure may be configured to produce a focused electronfield having any suitable cross-sectional profile or shape such as, forexample, a substantially circular, square, rectangular, triangular,ovate, or elliptical shaped cross-sectional profile, or anothercross-sectional profile of any other suitable bounded shape. In certainnon-limiting embodiments, an auxiliary ion plasma electron emitter, suchas an auxiliary wire-discharge ion plasma electron emitter according tothe present disclosure may generate a field of electrons having asubstantially rectangular-shaped cross-sectional profile (see FIGS. 13and 14) or a substantially circular-shaped cross-sectional profile (seeFIG. 15). Referring to FIG. 13, an auxiliary ion plasma electron emitter802 may include an ionization or a plasma region, similar to plasmaregion 314 of FIG. 4, that includes a wire anode or an electricallyconductive thin plate, sheet, or foil anode 819 (together 819)configured to produce a cation-containing plasma, and a cathode region,similar to cathode region 316 of FIG. 4, that includes a cathode 818.The cathode 818 may have any suitable shape. The plasma region may befilled with an ionizable gas at low pressure, and the gas may be ionizedin the plasma region to produce the cation-containing plasma. Forexample, the plasma region may be filled with helium gas at, forexample, approximately 20 mTorr. A small diameter wire anode or anelectrically conductive thin plate, sheet, or foil anode 819 may besituated within the plasma region. This anode 819 may have any suitableshape, although a rectangular configuration is shown in FIG. 13. Apositive voltage may be applied to the anode 819 by a high voltage powersupply 822, initiating ionization of the helium gas into a plasmacomprising helium cations and free “primary” electrons. Once ionizationof the helium gas is initiated, the plasma is sustained by applying avoltage to the anode 819. Positively charged helium ions within theplasma are extracted from the plasma region through an extraction grid,similar to extraction grid 326 of FIG. 4, maintained at a high negativeelectrical potential, and accelerated through a high voltage gap,similar to high voltage gap 328 of FIG. 4, into the cathode region,where the cations in the plasma impact the cathode 818 maintained at ahigh negative voltage. The cathode 818 may be, for example, a coated oruncoated metal or alloy. In one non-limiting embodiment, the cathode 818may comprise an insert having a high melting temperature and a low workfunction. A high voltage power supply, such as the high voltage powersupply 522 of FIG. 6, imparts a negative voltage greater than 20,000volts, for example, on the cathode 818.

Impingement of helium cations onto the cathode 818 releases secondaryelectrons from the cathode 818, thereby forming the focused electronfield. The high voltage gap accelerates the secondary electrons in adirection opposite the direction of movement of the helium cations,through the extraction grid and into the plasma region (through theelectrically conductive plate, sheet or foil, if present), and thenthrough a thin metallic foil window, if present, similar to the thinmetallic foil window 329 of FIG. 4, made of material relativelytransparent to electrons. As noted above, depending on the relative gaspressures within the auxiliary electron emitter and the melting furnacechamber, it may be possible to omit the electron-transmissive window, inwhich case the electrons produced by the auxiliary electron emitterwould enter the melting furnace vacuum chamber directly.

Still referring to FIG. 13, in one non-limiting embodiment positive ionsfrom the anode 819 may be accelerated to impinge on the cathode 818 tocreate a focused electron field having a cross-sectional profile that isrectangular-shaped or substantially rectangular-shaped. Therectangular-shaped or substantially rectangular-shaped anode 819 and thecathode 818 may be designed and arranged to better promote transmissionof the positively charged helium ions to the cathode 818. Also, thecathode 818 and the extraction grid may be designed and arranged tomaximize secondary electron transmission through the extraction grid andwith a field profile suitable for penetration through theelectron-transmissive window, if present (and the electricallyconductive thin plate, sheet or foil anode, if present). The focusedfield of energetic electrons exiting the auxiliary electron emitter 802may be directed to impinge on a target within the vacuum chamber of amelting furnace. Also, the electron-transmissive window, if present, maybe sized to be as thin as possible in order to maximize electrontransmission from the auxiliary ion plasma electron emitter 802. Analuminum-type or titanium-type foil having a thickness allowingsufficient electron transmission, while also maintaining a soft vacuumenvironment within the auxiliary ion plasma electron emitter 802, may beused as the foil window, if necessary. Other suitably strong andacceptable electron transparent materials that may be used as a windowin the apparatus, if present, will be known to those having ordinaryskill in the art. As discussed generally herein, the window may beomitted if the pressure difference between the interior of the auxiliaryelectron emitter 802 and the vacuum chamber containing the target is notsignificant.

In one embodiment, referring to FIG. 14, an auxiliary ion plasmaelectron emitter 902 may include certain features similar to those ofthe auxiliary ion plasma electron emitter 802. The auxiliary electronemitter 902, however, includes a rectangular-shaped or substantiallyrectangular-shaped wire anode or electrically conductive thin plate,sheet, or foil anode (together 919) positioned within a plasma region,and a rectangular-shaped or substantially rectangular-shaped cathode 918within a cathode region. Positive ions from the anode 919 may beaccelerated toward the cathode 918 to create a focused electron fieldhaving a cross-sectional profile that is rectangular-shaped orsubstantially rectangular-shaped and is configured for impingement onany condensate, solidified portions, or unmelted portions of materialwithin the melt, and/or onto regions of a forming or solidifying ingot.The auxiliary electron emitter 902 may also comprise a power supplyconfigured to supply a positive voltage to the anode 919. Although notillustrated, it will be understood that the cathode 918 will beconnected to a power supply configured to charge the cathode 918 to ahigh negative voltage.

In one embodiment illustrated in FIG. 15, an auxiliary electron emitter1002 according to the present disclosure may include certain featuressimilar to those of the auxiliary electron emitters 802 and 902. Theauxiliary electron emitter 1002, however, includes a circular-shaped, orsubstantially circular-shaped, wire anode or an electrically conductivethin plate, sheet, or foil anode (together 1019) positioned within aplasma region and a circular-shaped, or substantially circular-shaped,cathode 1018 positioned within a cathode region. Positive ions from theanode 1019 may be accelerated toward the cathode 1018 to create afocused electron field having a cross-sectional profile that iscircular-shaped or substantially circular-shaped and configured forimpingement on any condensate, solidified portions or unmelted portionswithin the melt, and/or onto regions of a forming or solidifying ingot.The auxiliary electron emitter 1002 may also comprise a power supplyconfigured to supply a positive voltage to the anode 1019. Although notillustrated, it will be understood that the cathode 1018 will beconnected to a power supply configured to charge the cathode 1018 to ahigh negative voltage.

The power of the various auxiliary electron emitters according to thepresent disclosure is dependent on the density of the cations producedby the anode and the negative voltage of the cathode. The number of ionscreated during ionization is dependent on the voltage applied to theanode (i.e., a higher voltage generates a greater number of ions perunit time and increases the density of a produced electron field), andthe energy of the electrons within the focused electron field isdependent on the negative voltage of the cathode. While not intending tobe bound by any particular theory, the inventor believes that meltingcondensate within the vacuum chamber will be facilitated by utilizing afocused electron field having relatively high power (e.g., electrondensity and electron energy) because there may be limited residence timeavailable in a particular region of the vacuum chamber for anycondensate to be melted before the condensate is flowed within the meltinto another region of the vacuum chamber. The same or a similar theoryapplies to melting solidified or unmelted portions within the melt.

In one non-limiting embodiment, an apparatus for melting an electricallyconductive metallic material comprises a vacuum chamber, a hearthdisposed in the vacuum chamber, and a melting device configured to meltthe electrically conductive metallic material. The apparatus may alsocomprise at least one of a mold, a casting apparatus, and an atomizingapparatus in communication with the vacuum chamber and positioned toreceive molten, electrically conductive metallic material from thehearth. The apparatus may comprise an auxiliary ion plasma electronemitter disposed in or adjacent to the vacuum chamber and positioned todirect a focused electron field having a cross-sectional area into thevacuum chamber. The focused field of electrons may have sufficientenergy to at least one of melt or re-melt portions of the electricallyconductive metallic material, melt solid condensate within theelectrically conductive metallic material, and heat regions of asolidifying ingot when directed toward the electrically conductivematerial, the solid condensate, and the regions of a solidifying ingotusing a steering device or system. In one non-limiting embodiment, themelting device comprises at least one ion plasma electron emitterdisposed in or adjacent the vacuum chamber and positioned to direct awide area electron field into the vacuum chamber. The wide-area electronfield may have sufficient energy to heat the electrically conductivemetallic material to its melting temperature. In another non-limitingembodiment, the melting device may comprise at least one thermo-ionicelectron beam gun configured to emit an electron beam having sufficientenergy to heat the electrically conductive metallic material to itsmelting temperature.

In one non-limiting embodiment, the auxiliary ion plasma electronemitters may be used with a melting furnace including one or morethermo-ionic electron beam guns. In view of the fact that a meltingfurnace using thermo-ionic electron beam guns generally has a vacuumchamber having a pressure much lower (e.g., 10³ to 7.5μ (10³ to 1 Pa) to15μ (2 Pa)) than a pressure of a melting furnace using ion plasmaelectron emitters (e.g., pressures greater than 40μ (5.3 Pa)), orpressures greater than 300μ (40 Pa)), an electron transmissive foil,such as the electron transmissive foil 705 of FIG. 10, for example, maybe positioned between the auxiliary electron emitter 700′ and the vacuumchamber 214 to maintain the separate pressures in the vacuum chamber 214and the auxiliary electron emitter 700′, for example. As such, thevarious auxiliary electron emitters may be used with a melting furnaceincorporating one or more thermo-ionic electron beam guns and/or othersuitable melting devices regardless of the operating pressure of themelting furnace. In various embodiments, any suitable number ofauxiliary ion plasma electron emitters can be used in one meltingfurnace.

In one non-limiting embodiment, a method of generating an electron fieldto melt an electrically conductive material within a melting furnace isprovided. The method may comprise providing an anode having a firstnon-linear shape, applying a voltage to the anode, and producing aplasma containing positive cations at the anode. The term “non-linearshape” can mean a shape other than a straight line or a substantiallystraight line. The term “non-linear shape” can also mean having a shapeother than the shape of the various electrodes discussed above, such asthe elongate wire electrode 516, for example. The method may furthercomprise providing a cathode having a second shape, positioning thecathode relative to the anode, and applying a voltage to the cathode.The voltage may be configured to negatively charge the cathode. Themethod may further comprise accelerating the positive cations toward thecathode to generate free secondary electrons, and forming the electronfield using the free secondary electrons. The electron field may have across-sectional profile with a third shape. The third shape of theelectron field may correspond to the first non-linear shape of the anodeand/or the second shape of the cathode. In one embodiment, the thirdshape of the electron field may be substantially the same as the firstnon-linear shape of the anode and/or the second shape of the cathode. Invarious embodiments, the anode may comprise an electrically conductiveelongate wire anode, an electrically conductive thin plate anode, anelectrically conductive thin sheet anode, or an electrically conductivethin foil anode.

In one non-limiting embodiment, a method of processing a material maycomprise introducing a material comprising at least one of a metal and ametallic alloy into a furnace chamber maintained at a low pressurerelative to atmospheric pressure and generating a first electron fieldhaving a first cross-sectional area using a first ion plasma electronemitter. The material within the furnace chamber may then be subjectedto the first electron field to heat the material to a temperature abovea melting temperature of the material. The method may also comprisegenerating a second electron field having a second cross-sectional areausing a second ion plasma electron emitter. At least one of solidcondensate within the material, solidified portions of the material, andregions of a solidifying ingot may be subjected to the second electronfield, using a steering device, to melt or heat the particular target.Also, the first cross-sectional area of the first electron field may belarger or otherwise different than the second cross-sectional area ofthe second electron field. The pressure within the first ion plasmaelectron emitter and the second ion plasma electron emitter may bemaintained at the same or substantially the same pressure as existswithin the furnace chamber. In other non-limiting embodiments, thepressure within the furnace chamber may be maintained at a pressure lessthan a pressure within the first ion plasma electron emitter and thesecond ion plasma electron emitter, for example.

In another non-limiting embodiment, a method of processing a materialmay comprise introducing a material comprising at least one of a metaland a metallic alloy into a furnace chamber maintained at a low pressurerelative to atmospheric pressure and subjecting the material within thefurnace chamber to a melting device configured to heat the material to atemperature above a melting temperature of the material. The method mayalso comprise generating a focused electron field using an auxiliary ionplasma electron emitter and subjecting at least one of any condensatewithin the material, any solidified portions of the material, andregions of a forming or solidifying ingot to the focused electron field,using a steering device, to melt or heat at least one of the condensate,the solidified portions, and the regions of the forming or solidifyingingot. In various non-limiting embodiments, the melting device maycomprise at least one thermo-ionic electron beam gun or at least one ionplasma electron emitter.

In still other non-limiting embodiments, a method of processing amaterial may comprise generating a focused electron field including across-sectional profile having a first shape using an auxiliary ionplasma electron emitter and steering the focused electron field toimpinge the focused electron field on the material and melt or heat atleast one of any solid condensate within the material, any solidifiedportions of the material, and/or regions of a forming or solidifyingingot. The method may also comprise generating the focused electronfield using an electrode having a second shape and a cathode having athird shape, wherein the first shape is substantially similar to thesecond shape and/or the third shape. In one non-limiting embodiment, thegenerated focused electron field emitted from the auxiliary ion plasmaelectron emitter may have one of a substantially circular-shapedcross-sectional profile and a substantially rectangular-shapedcross-sectional profile. Such focused electron fields may be generatedusing a substantially circular-shaped electrode or anode and asubstantially circular-shaped cathode or a substantiallyrectangular-shaped electrode or anode and substantiallyrectangular-shaped cathode, for example.

Although the foregoing description has necessarily presented only alimited number of embodiments, those of ordinary skill in the relevantart will appreciate that various changes in the apparatus and methodsand other details of the examples that have been described andillustrated herein may be made by those skilled in the art, and all suchmodifications will remain within the principle and scope of the presentdisclosure as expressed herein and in the appended claims. For example,although the present disclosure has necessarily only presented a limitednumber of embodiments of electron beam melting furnaces according to thepresent disclosure, and also has necessarily only discussed a limitednumber of ion plasma electron emitter and auxiliary ion plasma electronemitter designs, it will be understood that the present disclosure andassociated claims are not so limited. Those having ordinary skill, uponconsidering the present disclosure, will readily identify additional ionplasma electron emitter and auxiliary ion plasma electron emitterdesigns and may comprehend additional furnace designs along the linesand within the spirit of the necessarily limited number of embodimentsdiscussed herein. It is understood, therefore, that the presentinvention is not limited to the particular embodiments disclosed orincorporated herein, but is intended to cover modifications that arewithin the principle and scope of the invention, as defined by theclaims. It will also be appreciated by those skilled in the art thatchanges could be made to the embodiments above without departing fromthe broad inventive concept thereof.

What is claimed is:
 1. A method of processing an electrically conductivemetallic material, the method comprising: introducing an electricallyconductive metallic material comprising at least one of a metal and ametallic alloy into a furnace chamber maintained at a low pressurerelative to atmospheric pressure; generating a first electron fieldhaving a first area of coverage using at least a first ion plasmaelectron emitter; subjecting the material within the furnace chamber tothe first electron field to heat the material to a temperature above amelting temperature of the material; generating a second electron fieldhaving a second area of coverage using a second ion plasma electronemitter; and subjecting at least one of any solid condensate within thefurnace chamber, any solidified portions of the electrically conductivemetallic material, and regions of a solidifying ingot to the secondelectron field, using a steering system, to melt or heat at least one ofthe solid condensate, the solidified portions, and the regions of thesolidifying ingot, wherein the second area of coverage is smaller thanthe first area of coverage.
 2. The method of claim 1, wherein theelectrically conductive metallic material comprises at least one oftitanium, titanium alloys, tungsten, niobium, tantalum, platinum,palladium, zirconium, iridium, nickel, nickel base alloys, iron, ironbase alloys, cobalt, and cobalt base alloys.
 3. The method of claim 1,further comprising: forming a casting or a powder from the electricallyconductive metallic material subsequent to or simultaneous withsubjecting the material to at least the first electron field.
 4. Themethod of claim 1, further comprising: introducing at least oneelectrically conductive material selected from the group consisting oftitanium, titanium alloys, tungsten, niobium, tantalum, platinum,palladium, zirconium, iridium, nickel, nickel base alloys, iron, ironbase alloys, cobalt, and cobalt base alloys into the furnace chamber;optionally adding at least one alloying additive to the material; andforming a casting or a powder from the material subsequent to orsimultaneous with subjecting the material to the first electron field.5. The method of claim 1, further comprising maintaining a pressurewithin the first ion plasma electron emitter and the second ion plasmaelectron emitter which is substantially the same as a pressure withinthe furnace chamber.
 6. The method of claim 1, further comprisingmaintaining a pressure within the furnace chamber which is lower than apressure within the first ion plasma electron emitter and the second ionplasma electron emitter.
 7. The method of claim 1, further comprisingmaintaining a pressure within the furnace chamber greater than 40μ todecrease or eliminate undesirable evaporation of volatile elements fromthe material during heating of the material in the furnace chamber. 8.The method of claim 1, further comprising maintaining a pressure withinthe furnace chamber greater than 300μ to decrease or eliminateundesirable evaporation of volatile elements from the material duringheating of the material in the furnace chamber.
 9. The method of claim1, further comprising rastering the second electron field over one ofthe solid condensate, the solidified portions, and the regions of thesolidifying ingot to melt or heat one of the solid condensate, thesolidified portions, and the regions of the solidifying ingot.
 10. Themethod of claim 1, further comprising directing the second electronfield towards one of the solid condensate, the solidified portions, andthe regions of the solidifying ingot using a magnetic steering system.11. The method of claim 1, wherein the second electron field has one ofa substantially circular-shaped area of coverage and a substantiallyrectangular-shaped area of coverage.
 12. A method of processing anelectrically conductive metallic material, the method comprising:introducing an electrically conductive metallic material comprising atleast one of a metal and a metallic alloy into a furnace chambermaintained at a low pressure relative to atmospheric pressure;subjecting the material within the furnace chamber to a melting deviceconfigured to heat the material to a temperature above a meltingtemperature of the material; generating a focused electron field usingan auxiliary ion plasma electron emitter: and subjecting at least one ofany solid condensate within the furnace chamber, any solidified portionsof the material, and regions of a solidifying ingot to the focusedelectron field, using a steering system, to melt or heat at least one ofthe solid condensate, the solidified portions, and the regions of thesolidifying ingot.
 13. The method of claim 12, wherein the meltingdevice comprises at least one thermo-ionic electron beam gun configuredto emit an electron beam.
 14. The method of claim 12, wherein themelting device comprises at least one ion plasma electron emitter.
 15. Amethod of processing a material, comprising: generating a focusedelectron field including an area of coverage having a first shape usingan auxiliary ion plasma electron emitter; and steering the focusedelectron field to impinge the focused electron field on the material andmelt or heat at least one of any solid condensate within the material,any solidified portions of the material, and regions of a solidifyingingot.
 16. The method of claim 15, further comprising generating thefocused electron field using an electrode having a second shape and acathode having a third shape, wherein the first shape is substantialsimilar to at least one of the second shape and the third shape.
 17. Themethod of claim 15, further comprising generating the focused electronfield having one of a substantially circular-shaped area of coverage anda substantially rectangular-shaped area of coverage using the auxiliaryion plasma electron emitter.
 18. The method of claim 17, furthercomprising generating the focused electron field using a substantiallycircular-shaped electrode and a substantially circular-shaped cathode.19. The method of claim 17, further comprising generating the focusedelectron field using a substantially rectangular-shaped electrode andsubstantially rectangular-shaped cathode.
 20. A method of generating anelectron field to melt an electrically conductive material within amelting furnace, the method comprising: providing an anode having afirst non-linear shape; applying a voltage to the anode; producing aplasma containing positive cations at the anode; providing a cathodehaving a second shape; positioning the cathode relative to the anode;applying a voltage to the cathode, wherein the voltage is configured tonegatively charge the cathode; accelerating the positive cations towardthe cathode to generate free secondary electrons; and forming theelectron field using the free secondary electrons, the electron fieldhaving an area of coverage with a third shape, wherein the third shapecorresponds to the first non-linear shape of the anode.
 21. The methodof claim 20, wherein the third shape of the electron field correspondsto the second shape of the cathode.
 22. The method of claim 21, whereinthe third shape of the electron field is substantially the same as thesecond shape of the cathode.
 23. The method of claim 20, wherein theanode comprises one of a wire, an electrically conductive thin plate, anelectrically conductive thin sheet, and an electrically conductive thinfoil.
 24. The method of claim 20, wherein the third shape of theelectron field is substantially the same as the first non-linear shapeof the anode.